The statements in this section merely provide background information related to the present teachings and may not constitute prior art.
Ink jet print heads tend to be sensitive to bumping or jolting. This relates to the fact that there is very sensitive control on the ink meniscus at the nozzle orifice. This bumping and jolting can occur when the head is moved up and down for cleaning or to re-thread the substrate. If a print head is jolted too much, then the meniscus can be lost and air becomes entrapped into the nozzle orifice resulting in missing jets. Loss of jets in a single pass printing activity can cause print quality defects, which are generally not acceptable. This is worse in some print heads, such as the grayscale print heads, which are very sensitive to loss of jets when jolted or vibrated, but occurs to some extent in all ink jet heads.
Little has been done in the past to adequately resolve this problem. Systems tend to be fitted with air driven or manual actuators which move the print heads up and down. This technique does tend to improve the control of head movement over a more manual process, but has proven to be insufficient. Air actuators are especially vulnerable to reduced motion quality with time.
Separate from the above issue, ink jet print systems often rely upon the extremely precise placement of their print heads. If the print heads can be accurately aligned and secured, it is then possible to set two heads in relation to each other such that the nozzle ports are “interleaved”. This interleaved configuration results in a doubling of the print dot density, so that two heads, each with 150 dots per inch (DPI) resolution, can print like a single 300 DPI print head.
Aside from achieving the interleaved configuration described above, print heads are commonly placed side by side to gain additional print width. Print heads can be “stitched” together in this manner to create wide format printers made up of a series of narrow heads that have been stitched together. The accuracy with which the heads are stitched together must also be high as it is not generally acceptable to have either a gap or and overlap in the printed image. For these reasons and others around print quality, the ability to secure and align print heads in the system may be important to functionality.
Previous work to interleave and stitch print heads together have centered on a trial and error methodology, whereby prints are generated and visually checked (under a low power microscope) for interleave and stitch accuracy. If the prints show a misalignment condition, the heads are loosened, moved to a new location, and re-tightened. This method is repeated until all heads are interleaved and stitched properly. It should be appreciated that this process is very time consuming, since moving one head necessitates moving all other heads as their locations are interrelated. Other methods that use an optical alignment tool to interleave two heads together use non-reversible adhesives to bond the heads together. This method has the inherent risk such that if the alignment is not accurate after the bond is set, no corrections can be made, and thus, the heads must be scrapped.
Still further, industrial ink jet printing systems often rely on a smooth support surface to support the substrate in the web zone where printing is being done (where the ink jets are jetting). This requirement is to maintain the optimized distance between the substrate and the print heads.
Print platens are commonly designed and manufactured to be smooth, flat surfaces, slightly wider than the substrate itself, and long enough to accommodate the print zone length. The substrate is transported to and from the print platen by a series of web rollers incorporated into the printer.
During printing, some substrates tend to curl up along the edges. This is especially true if the substrate is made of multiple layers, e.g., a pressure sensitive adhesive label stock with a printable top surface, adhesive layer, and a removable backing paper. Such substrates tend to curl at the edges regardless of increasing speed or tension. It should be readily appreciated that this curling action changes the physical position of that portion of the substrate in relation to the print heads, which results in poor print quality along the edges or significant reduction in printable width for a given substrate width.
Conventional designs of print platens have primarily centered on full surface flat plates or full surface curved surfaces. However, flat platen designs do not address the curled substrate issue. Conversely, full surface curved platens are cost prohibitive because of the challenging machining that is required to manufacture.
Finally, the sustainability, jetting quality, and ultimate print quality of the ink used in digital ink jet printing are affected when the temperature of the ink is not accurately controlled prior to entering the print head. Although methods of thermal conditioning have been used before, the techniques according to the present teachings show significant improvement.
Previous work to control the temperature of the ink was mostly limited to the use of the water jacket or an electric heater attached to a print head. However, such techniques failed to provide effective and reliable results.